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. 2018 Jul;6(4):301-311.

Early Results of Oxford Mobile Bearing Medial Unicompartmental Knee Replacement (UKR) with the Microplasty Instrumentation: An Indian Experience

Sahil Gaba  1   2 , Naman Wahal  1   2 , Deepak Gautam  1   2 , Hemant Pandit  1   2 , Vijay Kumar  1   2 , Rajesh Malhotra  1   2
Affiliations

Early Results of Oxford Mobile Bearing Medial Unicompartmental Knee Replacement (UKR) with the Microplasty Instrumentation: An Indian Experience

Sahil Gaba et al. Arch Bone Jt Surg. 2018 Jul.

Abstract

Background: Oxford medial unicompartmental knee replacement (UKR) is indicated in patients with anteromedial osteoarthritis (AMOA) of the knee. Microplasty (MP) instrumentation was introduced in 2012 as an improvement over phase 3 instrumentation. Advantages of this instrumentation include conservative tibial cut, decreased tibial re-cut rate and improved component alignment. We report the results of UKR with the new instrumentation in a consecutive series with a minimum follow-up of 2 years.

Methods: A prospective study of 115 cemented medial Oxford UKRs implanted in 89 patients was done. Post-operative alignment of the tibial and femoral components was analysed. Patient reported outcome measures were recorded using Oxford Knee Score (OKS) and the American Knee Society Score (KSS). Tegner Activity Scale (TAS) was used to record the activity level.

Results: 115 consecutive medial Oxford UKRs were studied. All patients were followed up annually in this prospective ethically approved study. The mean follow-up was 36 months and the minimum follow-up was 25 months. No patient died and none were lost to follow-up. At the final follow-up, the average OKS of the cohort was 39.5 (SD: 5.7). 91.2 % of the patients had good or excellent OKS with only 3.5 % reporting poor OKS. The overall limb alignment was 4.80 varus (0 - 140 varus). Tibia was recut in 5.2 % of cases. Median bearing size was 3 (range: 3 to 6). There was one case of bearing dislocation and one case of aseptic tibial loosening.

Conclusion: This is the first study to report results of MP instrumentation at a minimum follow-up of 2 years. Our study indicates that the new instrumentation results in reliable and accurate implantation of femoral and tibial components in majority of the cases, with a decrease in number of alignment outliers, and also a reduced rate of bearing dislocation.

Keywords: Anteromedial osteoarthritis (AMOA); Microplasty instrumentation; Mobile bearing; Unicompartmental knee replacement (UKR).

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Figures

Figure 1
Figure 1
Intra-operative photograph showing intact cartilage in lateral compartment and an intact ACL
Figure 2
Figure 2
Method of marking flexion-extension axis on tibia using an osteotome. The vertical tibial cut should be parallel to this mark.
Figure 3
Figure 3
Femoral sizing stylus (Extra small) in place showing 5 mm space between condyle and stylus due to eburnated bone.
Figure 4
Figure 4
Tibial assembly in place showing the G clamp connecting the extramedullary tibial jig with the stylus.
Figure 5
Figure 5
Marking the centre of medial femoral condyle.
Figure 6
Figure 6
Intramedullary rod and femoral cutting guide linked with the IM linker. The drill slots in the guide must line up with the central mark on medial femoral condyle.
Figure 7
Figure 7
Final components and bearing in place. Ideally, a thin osteotome must easily pass between the bearing and the tibial tray. This ensures that bearing will not impinge on the tibial tray.
Figure 8
Figure 8
AP and lateral radiographs of a case showing meniscal dislocation. The dislocation was a result of trauma. Arrow points towards the bearing location.
Figure 9
Figure 9
Intra-operative photograph of the dislocated bearing lying medially in the suprapatellar space. The bearing was a size 3, and was replaced by a size 5 bearing based on stability during trial.
Figure 10
Figure 10
AP and lateral radiographs of a patient with aseptic loosening of the tibia.
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